Big storms challenge aging sewer systems

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By Tom Saul | Wednesday, May 16, 2007 3:35 PM CDT | () comments

Signs along the levee in downtown Rock Island warn people to stear clear of the outfalls when is rains.

When the spring rains come, Rock Island’s aging combination of storm and sanitary sewers can flush untreated sewage into the Mississippi River.

Outfalls along the levee that protect the riverside city from flooding clearly mark the places where a slurry of stormwater runoff and untreated sewage could spew if the municipal sewage treatment plant is overwhelmed during a storm.

“We have about five or six overflows per month during wet weather,” said Dale Howard, the city’s utilities superintendent. “The stormwater mixes with the sewage, so it dilutes it somewhat, but untreated sewage does go into the river.”

The same is true of the regional treatment plant in southwest Davenport that serves Davenport, Bettendorf, Riverdale and Pleasant Valley. Overflows are not a regular occurrence, but stormwater runoff can lead to untreated sewage entering the river. It can happen when stormwater gets into sanitary sewer lines because they are combined with storm lines or because of breaks caused by any number of factors.

The latest incident occurred in late April when a storm that pushed three times the normal amount of effluent through the plant. That problem combined with a power outage to dump 100,000 gallons of stormwater mixed with raw sewage that found its way into the river, said Dennis Ryan, plant manager.

Overflows are a greater problem in older cities, such as Davenport and Rock Island, where underground infrastructure is older and in poorer shape and where there are combined storm and sanitary sewers, say environmental regulators and city officials. Construction of combined systems have been prohibited for years, and if such a system is replaced, storm and sanitary lines must be separated.

The U.S. Environmental Protection Agency requires cities to take steps to reduce the possibility of overflow pollution caused by combined sewer systems, according to an agency report. It stresses storage of effluent until it can be treated, preventative maintenance and pollution prevention programs. It also requires long-term planning for system improvements to eliminate combined systems.

“In many cases, states have adopted the federal rules at the state level that disallow overflow pollution into rivers and streams,” said Barbara Lynch, bureau chief of field services for the Iowa Department of Natural Resources, which regulates discharges into Iowa waters.

Although much of the raw sewage is diluted because it is mixed with stormwater and it is discharged into waterways that are swollen with rain water, the effluent still contains pathogens that can be harmful to people and animals, Lynch said.

During its 2008 fiscal year, Davenport plans to start construction to replace its last major segment of combined sewer system along Rockingham Road, said Dee Bruemmer, the city’s public works director. Among the purposes of a $49.3 million sewer tunnel planned for west Davenport are to increase the city’s ability to store sewage during heavy rains.

In the case of Rock Island, the federal EPA has taken a hard stance. In 2000, it sued the city over the issue of combined sewer outflow into the river. Under a consent decree, the city is awaiting the agency’s approval of a $56 million plan to eliminate combined sewer systems, Howard said.

Moline has few problems with overflows, said Dennis Webb, the city’s water pollution control general manager. It has twin plants serving the north and south portions of the city. The south plant is capable of holding and re-treating overflows in the event of a heavy rain.

“The north plant at the very least gets gravity settling and chlorination, so we don’t discharge any untreated sewage into the river,” Webb said. “As long as everything functions as it is supposed to, we don’t discharge untreated sewage.”

Tom Saul can be contacted at (563) 383-2453 or tsaul@qctimes.com. Comment on this story at www.qctimes.com.

SEWER PROJECTS

Municipalities in the Quad-Cities are either planning or building projects aimed at separating storm and sanitary sewers so raw sewage does not flow into area streams and rivers during heavy rains.

Davenport — Will spend $2.5 million during the next fiscal year to separate storm and sanitary sewers on a portion of Rockingham Road between Schmidt Road and Birchwood Avenue and is making plans for a $49.3 million sewage diversion tunnel in west Davenport.

Bettendorf — Is spending $250,000 to separate the last two combined storm and sanitary sewers in the city. One is located on 8th and 10th streets and the other is 6th Street.

Rock Island — Is awaiting approval by the U.S. Environmental Protection Agency of a $56 million plan to separate combined storm and sanitary sewers in the city.